This invention relates to the measuring of toner remaining in cartridges and other toner containers used in imaging, such as printing and copying.
Measuring the amount of toner available in a printer or copier is useful. Such information can be presented to the printer or copier user so that the user can plan cartridge purchases or otherwise plan future use of the imaging device.
Toner is currently measured in a variety of ways, such as by sensing the resistance of a toner paddle which rotates in a toner hopper or sensing toner optically through a window of transparent material in the side of the hopper or other container. Another method employs the weight of the toner to measure its amount.
Since toner takes any number of configurations during use, such as being piled against one side of its container or uneven on it surface, most techniques for measuring toner amount can not compensate fully for the different configurations and are therefore significantly inaccurate. Measuring toner weight does avoid the effects of the different configurations, but requires the entire container, such as a toner cartridge to be accurately weighed.
This invention measures air in the toner container to measure toner amount in an inexpensive way and which avoids the effects of the different configurations.
As escape of toner would soil the user, toner is necessarily kept in a closed container from which air does not readily escape. In such a container, at least one responsive member is located in an upper wall above the toner. The volume of the closed container, which is filled with air and toner, is perturbed and the pressure response of air in the container is observed. Boyles Law inversely relates the volume of air to pressure with pressure times volume being constant.
In the preferred embodiment a diaphragm consisting of a flexible member and a permanent magnet is used to excite the volume of air using a magnetic coil. The excitation can be by a single pulse of current to an exciting coil, in which case the ringing motion of the magnet can be measured using the current response of the coil. Alternately, the excitation can be via a frequency sweeping of sinusoidal current to the exciting coil and the frequency with maximum amplitude used to determine the resonant frequency. The volume of air acts like a spring and the diaphragm-magnet assembly acts as both a mass and a spring in a mass spring system which inherently seeks its resonant frequency, and the resonant frequency is a function of the inverse of the square root of the volume of air in the closed container. As the total volume of the container is known, the volume of toner is directly found as the total volume less the volume of the air measured.
Also, preferably, the subsequent movement of the diaphragm to resonant oscillation is observed through the driven coil, which now generates a current in response to the motion of the magnet mounted to the diaphragm.